This invention relates to an equipment for cleaning, etching and drying a semiconductor wafer and a method of using it.
In a general process of manufacturing a semiconductor device, particles, heavy metal such as iron, copper, nickel, chromium, light metal such as aluminum, alkali metal such as sodium, potassium, calcium, and various kinds of micro grains result lower production yield, thus they must be reduced. A process of cleaning a semiconductor wafer is the key for reducing the particles. For cleaning the wafer, an equipment for immersing wafer in chemical, namely a dip-type cleaner is mainly used, in which RCA cleaning solutions (mixed solution SC1 of aqueous ammonium, hydrogen peroxide and ultrapure water, mixed solution SC2 of hydrochloric acid, hydrogen peroxide and ultrapure water, and mixed solution of hydrofluoric acid and ultrapure water) which are proposed by W. Kern in RCA Review, vol. 31, page 187, 1970, are widely used as a chemical for cleaning a wafer. Particularly, SC1 is excellent in removing particles and organic contamination, so as to be used in cleaning for removing particles. Also, SC2 is excellent in removing heavy metal and can be used in combination with SC1. For removing organic contamination, mixed solution of sulfuric acid and hydrogen peroxide is used.
Referring to a conventional dip-type cleaner, as shown in FIG. 8, a wafer d to be cleaned which is accommodated in a teflon cassette c is disposed on a mesh b within a bath a which is a container made of quartz or Teflon (PFA or the like) having chemical resistance, then a chemical introducing valve e is opened to introduce and fill a chemical in the bath a through a chemical introducing line f, thereby immersing the wafer d in the chemical in the bath a. In the cleaner, in order to reduce the chemical consumption, a chemical circulation line h is provided for returning the chemical, which is discharged from a drain port provided at the bottom of the bath a, into the bath a again after filtering by a filter g. After treating with the chemical, a ultrapure water introducing valve i is opened to introduce ultrapure water through an ultrapure water introducing line j into the bath a, thereby the chemical is cleaned out from the surface of the wafer d and from the bath a. Wherein, respective references k and l are three-way valves provided in the middle of the chemical circulation line h.
Referring to a series of operation sequence from cleaning to drying of a semiconductor wafer, as shown in FIG. 9, general steps are: cleaning it in the aforementioned dip-type cleaner D1 with the use of a first chemical; cleaning it in another cleaner D2 with the use of a second chemical; cleaning it in a bath E filled with ultrapure water; then drying it by a rotary drying equipment F utilizing centrifugal force or by organic-vapor drying with the use of hot vapor of isopropyl alcohol.
However, the wafer d is immersed in the chemical in the aforementioned dip-type cleaner, which requires large amounts of chemical and ultrapure water, while displaying remarkable power of removing particles and contaminant adhered to the wafer surface. According to plain calculation, chemical of about 65 litters is required for processing 50 wafers d of 200 mm diameter in the Teflon cassette c, and ultrapure water of about 40 litters per minute is required for water rinsing. To save the chemical in even a small amount, the chemical is reused by circulating and filtering it in a set cycle, which contaminates again the wafer surface, because the chemical once contaminated by impurities or by particles eluted thereinto cannot be cleaned even by filtering. Further, it is impossible to reuse circulated and filtered ultrapure water for water rinsing. The conventional operation sequence from cleaning to drying requires transportation of the wafer d among a plurality of baths and equipments D1, D2, E, F, which lowers operation efficiency and causes generation of stain or water marks, water spots due to exposure of the wafer to the air at transportation.
On the other hand, a spray-type cleaner is proposed for reducing used amounts of chemical and ultrapure water, in which the chemical or ultrapure water is sprayed from a spray nozzle to cleaning the wafer in the chamber, while rotating the wafer. The spray-type cleaner has advantages that no re-contamination by the chemical is involved with no circulation of the chemical and that equal or less amount of chemical is used compared with that in the dip-type cleaner employing the circulation and filtering. Moreover, much less amount of ultrapure water is required, compared with that in the dip-type cleaner.
However, the aforementioned spray-type cleaner cleans the wafer insufficiently, compared with the dip-type cleaner. For example, as suggested in the Institute of Electronics, Information and Communication Engineers (IEICE), Transactions On Electronics, vol E77-C, No. 3 (March, 1994), page 492 by Kawahara et al., to remove particles depends on etching amount of the wafer surface by SC1 cleaning solution, so that long time cleaning is required when the temperature of the chemical is low. In general, the temperature of the chemical can be set to 60-80.degree. C. at the highest and treatment time is about 1 or 2 minutes in the spray-type cleaner, which results in that the wafer surface of a silicon substrate can be etched to about 0.5-1 nm. As described above, according to the study by Kawahara et al., the silicon substrate must be etched to 4 nm for sufficient removal efficiency of particles, which is difficult for the spray-type cleaner or which leads to difficulty in attaining a decrease in chemical consumption which is the advantage of the spray-type cleaner. In addition, the spray-type cleaner also involves generation of water marks (stain) due to exposure of wafer to the air.